Grouper iridoviral disease

What is it?

The disease affects fry, juveniles, and one to two year old market-sized grouper.
Causative agent is a enveloped double-stranded DNA
(dsDNA) virus with a size of 160-200 nm in diameter. Viral replication occurs in the
cytoplasm of the infected cell and virus grows well in cultured fish cell lines derived
from grouper.

Where and When Might it Occur?

The disease has been officially reported from Hong Kong, Indonesia, the Republic of Korea, and Viet Nam.

The highest mortalities are usually seen in fish three to four month old, after
stocking into sea cages.

Horizontal contact and waterborne transmission appear to be the principal ways the virus is spread.

Diagnosis

Fish infected with the disease often become very lethargic and show a decrease in appetite. Fish may also preform rapid opercular movements, dashing to the surface for air. This often occurs in the later stages of the disease. High mortality often follows.

Fish may also show deep ulceration in muscular tissue and red boils on the body
surface.

Gross pathological signs are:

darkened body colour, pale gills and enlarged spleen

signs of secondary infection such as deep ulceration or papular lesions.

Microscopic pathological signs are:

necrosis of the splenic pulp and myocardium

necrosis and reduction of haematopoietic tissue.

Control/Treatment

There is currently no control method for the disease.

SOURCE: Australian Government, Department of Agriculture, Fisheries and Forestry